Phenolic Profile, Antioxidant Capacity and Antimicrobial Activity of Nettle Leaves Extracts Obtained by Advanced Extraction Techniques.

Ivona Elez Garofulić,Verica Dragović-Uzelac,Valentina Malin,Sonja Smole Možina,Maja Repajić,Meta Sterniša,Sandra Pedisić,Zoran Zorić

doi:10.3390/molecules26206153

Ivona Elez Garofulić, Verica Dragović-Uzelac + Show 6 more

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https://doi.org/10.3390/molecules26206153

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Abstract

Nettle is a widely known plant whose high biological activity and beneficial medicinal effects are attributed to various bioactive compounds, among which polyphenols play an important role. In order to isolate polyphenols and preserve their properties, advanced extraction techniques have been applied to overcome the drawbacks of conventional ones. Therefore, microwave-assisted extraction (MAE) has been optimized for the isolation of nettle leaves polyphenols and it was compared to pressurized liquid extraction (PLE) and conventional heat-reflux extraction (CE). The obtained extracts were analyzed for their individual phenolic profile by UPLC MS2 and for their antioxidant capacity by ORAC assay. MAE proved to be the more specific technique for the isolation of individual phenolic compounds, while PLE produced extracts with higher amount of total phenols and higher antioxidant capacity. Both techniques were more effective compared to CE. PLE nettle extract showed antimicrobial activity against bacteria, especially against Gram-negative Pseudomonas fragi ATCC 4973 and Campylobacter jejuni NCTC 11168 strains. This suggests that PLE is suitable for obtaining a nettle extract with antioxidant and antimicrobial potential, which as such has great potential for use as a value-added ingredient in the food and pharmaceutical industry.

Highlights

Nettle (Urtica dioica L.) is an annual plant belonging to the genus Urtica, family Urticaceae, that widespread in Europe, Asia, Africa and North America
According to the literature reports [13,19,20], 30% aqueous ethanol and acetone solutions have been considered as effective solvents for both conventional and advanced extraction techniques for the isolation of plant polyphenols and were compared with pure distilled water for their effectiveness in microwave-assisted extraction (MAE) of nettle leaves’
In comparison with conventional heat-reflux extraction (CE), optimized MAE and pressurized liquid extraction (PLE) as advanced extraction techniques showed to be fast and effective methods resulting in extracts with higher phenolic content and with higher antioxidant capacity

Summary

Introduction

Nettle (Urtica dioica L.) is an annual plant belonging to the genus Urtica, family Urticaceae, that widespread in Europe, Asia, Africa and North America. The plant has been traditionally used for medicinal purposes for centuries due to its great biological activity and beneficial effects on human health attributed to its antioxidant, antimicrobial, anti-inflammatory, anti-ulcer activity and analgesic properties [1]. These properties can be ascribed to diverse bioactive molecules present in nettle. Studies have confirmed the correlation between dietary intake of polyphenols, especially phenolic acids, flavonoids and tannins, and their health promoting effects arise from their potential to scavenge reactive species and prevent oxidative stress and inflammation [3,4]. Leaves are considered to be the richest part of the plant for their phenolic content. Zeković et al (2017) [5]

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